After 12 years without a crash of its cherished V-22 tilt-rotor aircraft, the Marines lost one Wednesday in Morocco. The accident killed two of the four Marines aboard during a training exercise, and the other two were severely injured.

After the V-22’s trouble birth and infancy, the revolutionary aircraft – rotating props and engines let it take off and land like a chopper, but fly long distances like a turboprop plane – has become the corps’ safest rotorcraft.

V-22 units have been deployed to Afghanistan and Iraq 13 times since becoming operational in 2007. An Air Force V-22 crashed in Afghanistan two years ago during an Army Ranger night raid, killing four of the 18 personnel on board.

Wednesday’s crash involved a V-22 Osprey assigned to the North Carolina-based 24th Marine Expeditionary Unit. It had flown from the amphibious ship USS Iwo Jima as part of a training mission involving 1,200 U.S. troops and 900 Moroccan forces in an exercise dubbed “African Lion” in the southern part of the country.

The aircraft was part of Marine Medium Tiltrotor Squadron (VMM) 261, based out of Marine Corps Air Station New River, N.C. The identity of those killed are being withheld until their families are notified.

While there were several V-22 crashes during its lengthy development, the last fatal Marine crash prior to Wednesday’s was in North Carolina on December 11, 2000 – 4,140 days ago. A hydraulic leak and software snafu sent the aircraft plunging to the ground, killing the four Marines aboard.